Grease Composition For Use In Constant Velocity Joints

ABSTRACT

In order to provide for a grease composition which has a good compatibility with boots made of rubber or thermoplastic elastomer, and which also gives low wear and low friction, a grease composition for use in constant velocity joints is suggested, comprising
         a) a base oil composition;   b) at least one tri-nuclear molybdenum compound of the formula       

       Mo 3 S k L n Q z ,         wherein L are independently selected ligands having organo groups with a sufficient number of carbon atoms to render the compound soluble or dispersible in the oil, n is from 1 to 4, k varies from 4 though 7, Q is selected from the group of neutral electron donating compounds such as amines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values;   c) at least one urea derivative thickener.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of International Patent Application No.PCT/EP2006/009718, filed Oct. 7, 2006, and which is incorporated in itsentirety by reference.

FIELD OF THE INVENTION

The present invention relates to a lubricating grease which is intendedprimarily for use in constant velocity universal joints, especially balljoints or tripod joints, which are used in the drivelines of motorvehicles.

BACKGROUND OF THE INVENTION

The motions of components within constant velocity joints (CVJ) arecomplex with a combination of rolling, sliding and spinning. When thejoints are under torque, the components are loaded together which cannot only cause wear on the contact surfaces of the components, but alsorolling contact fatigue and significant frictional forces between thesurfaces. The wear can result in failure of the joints and thefrictional forces can give rise to noise, vibration and harshness (NVH)in the driveline. NVH is normally “measured” by determining the axialforces generated in plunging type CVJ. Ideally the greases used inconstant velocity joints need not only to reduce wear, but also have tohave a low coefficient of friction to reduce the frictional forces andto reduce or prevent NVH.

Constant velocity joints also have sealing boots of elastomeric materialwhich are usually of bellows shape, one end being connected to the outerpart of the CVJ and the other end to the interconnecting or output shaftof the CVJ. The boot retains the grease in the joint and keeps out dirtand water.

Not only must the grease reduce wear and friction and prevent thepremature initiation of rolling contact fatigue in a CVJ, it must alsobe compatible with the elastomeric material of which the boot is made.Otherwise there is a degradation of the boot material which causespremature failure of the boot, allowing the escape of the grease andultimately failure of the CVJ. The two main types of material used forCVJ boots are polychloroprene rubber (CR) and thermoplastic elastomer(TPE), especially ether-ester block co-polymer thermoplastic elastomer(TPC-ET).

Typical CVJ greases have base oils which are blends of naphthenic(saturated rings) and paraffinic (straight and branched saturatedchains) mineral oils. Synthetic oils may also be added. It is known thatsaid base oils have a large influence on the deterioration (swelling orshrinking) of both boots made of CR and TPC-ET. Both mineral andsynthetic base oils extract the plasticisers and other oil solubleprotective agents from the boot materials, Paraffinic mineral oils andpoly-α-olefin (PAO) synthetic base oils diffuse very little intoespecially boots made of rubber material causing shrinkage, but on theother hand naphthenic mineral oils and synthetic esters diffuse intoboot materials and act as plasticisers and can cause swelling. Theexchange of plasticiser or plasticiser compositions for the naphthenicmineral oil can significantly reduce the boot performance, especially atlow temperatures, and may cause the boot to fail by cold cracking,ultimately resulting in failure of the CVJ. If significant swelling orsoftening occurs, the maximum high speed capability of the boot isreduced due to the poor stability at speed and/or excessive radialexpansion.

In order to solve the aforesaid problems, U.S. Pat. No. 6,656,890 B1suggests a special base oil combination comprising 10 to 35% by weightof one or more poly-α-olefins, 3 to 15% by weight of one or moresynthetic organic esters, 20 to 30% by weight of one or more naphthenicoils, the remainder of the combination being one or more paraffinicoils, and, further, a lithium soap thickener, and a sulphur-freefriction modifier, that may be a organo-molybdenum complex, andmolybdenum dithiophosphate, and a zinc dialkyldithiophosphate andfurther additives such as corrosion inhibitors, anti-oxidants, extremepressure additives, and tackiness agents. However, the frictioncoefficient and the wear of grease compositions according to U.S. Pat.No. 6,656,890 B1 as measured in SRV (abbreviation for the German wordsSchwingungen, Reibung, Verschleiβ) tests needs to be improved.

SUMMARY OF THE INVENTION

Thus, it is the object of the present invention to provide for a greasecomposition, primarily for use in constant velocity joints, which has agood compatibility with boots made of rubber or thermoplastic elastomer,and which also gives low wear and low friction in use in CVJ.

Said object of the present invention is solved by a grease compositionfor use in constant velocity joints comprising

a) a base oil composition; and

b) at least one tri-nuclear molybdenum compound, preferable 0.25% byweight to 5% by weight, more preferable 0.3% by weight to 3% by weight,referred to the total amount of the grease composition, of the formula

Mo₃S_(k)L_(n)Q_(Z),  (I)

wherein L are independently selected ligands having organo groups with asufficient number of carbon atoms to render the compound soluble ordispersible in the oil, n is from 1 to 4, k varies from 4 though 7, Q isselected from the group of neutral electron donating compounds such asamines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 andincludes non-stoichiometric values;

c) at least one urea derivative thickener;

The number of carbon atoms present in the tri-nuclear molybdenumcompound among all the ligands, organo groups is at least 21 carbonatoms, preferably at least 25, more preferably at least 30, and mostpreferably at least 35. Tri-nuclear molybdenum compounds usable in thepresent invention are disclosed in U.S. Pat. No. 6,172,013 B1, thedisclosure of which is incorporated in the present invention insofar byreference. The presence of at least 0.25% by weight of the tri-nuclearmolybdenum compound according to claim 1 is preferred and significantlylowers the friction coefficient as well as the wear when used in CVJ.

As a base oil composition according to the present invention, a base oilcomposition as disclosed in U.S. Pat. No. 6,656,890 B1, the disclosureof which is incorporated insofar herein by reference, may preferably beused. However, any further kind of base oil composition, especially ablend of mineral oils, a blend of synthetic oils or a blend of a mixtureof mineral and synthetic oils may be used. The base oil compositionshould preferably have a kinematic viscosity of between about 32 andabout 250 mm²/s at 40° C. and between about 5 and about 25 mm²/s at 100°C. The mineral oils preferably are selected from the group comprising atleast one naphthenic oil and/or at least one paraffinic oil. Thesynthetic oils usable in the present invention are selected from a groupcomprising at least one poly-α-olefin (PAO) and/or at least onesynthetic organic ester. The organic synthetic ester is preferably adi-carboxylic acid derivative having subgroups based on aliphaticalcohols. Preferably, the aliphatic alcohols have primary, straight orbranched carbon chains with 2 to 20 carbon atoms. Preferably, theorganic synthetic ester is selected from a group comprising sebacicacid-bis(2-ethylhexylester) (“dioctyl sebacate” (DOS)), adipicacid-bis-(2-ethylhexylester) (“dioctyl adipate” (DOA)), and/or azelaicacid-bis(2-ethylhexylester) (“dioctyl azelate” (DOZ)).

If poly-α-olefin is present in the base oil composition, preferablypoly-α-olefins are selected having a viscosity in a range from about 2to about 40 centistokes at 100° C. The naphthenic oils selected for thebase oil compositions have preferably a viscosity in a range betweenabout 20 to about 150 mm²/s at 40° C., whereas if paraffinic oils werepresent in the base oil composition, preferably the paraffinic oils havea viscosity in a range between about 25 to about 170 mm²/s at 40° C.

According to the present invention, the grease composition comprises atleast one urea derivative thickener. The urea derivative thickener usedin accordance with the present invention may also be a urea complexthickener, that is defined as a mixture of at least one urea derivativethickener with at least one other thickener not being a urea derivativethickener. Especially preferred urea complex thickeners in accordancewith the present invention are mixtures of at least one urea derivativethickener with at least one calcium and/or lithium-based thickenerand/or complex thickener.

As a urea-derivative type thickener in the present invention, especiallya urea thickener manufactured by the company Kyodo Yushi Co., Ltd.,Tokyo, Japan, is used as defined in U.S. Pat. No. 5,589,444. Theurea-derivative thickener is preferably a reaction product of at leastone organic aliphatic amine with at least one organic phenyl isocyanate.However, the urea-derivative thickener is not restricted to specificones and may be, for instance, also a diurea compound and/or a polyureacompound.

Examples of diurea compounds include those obtained from a reaction of amonoamine with a diisocyanate compound. Examples of useful diisocyanatesinclude phenylendiisocyanate, dephenyldiisocyanate, phenyldiisocyanate,dephenylmethandiisocyanate, octadecanediisocyanate, decanediisocyanate,and hexanediisocyanate. Examples of useful monoamines includeoctylamine, dodecylamine, hexadecylamine, octadecylamine, oliylamine,aniline, t-toluidine, and cyclohexylamine. Especially preferred diureacompounds are compounds obtained by reaction of(4,4′-methylenediphenyldisocyanate) (MDI) with octadecylamine.

Examples of useful polyurea compounds include those obtained from areaction of a diamine with a diisocyanate compound. Examples of usefuldiisocyanate include those used for the formation of the diureacompounds as mentioned above, whereas examples of useful diaminesinclude ethylendiamine, propanediamine, butanediamine, hexanediamine,octanediamine, phenylenediamine, tolylenediamine, and xylenediamine.Most preferred examples of urea type derivative thickeners include thoseobtained through a reaction of arylamine such as aniline or p-toluidine,cyclohexylamine or a mixture thereof with a diisocyanate. The aryl groupin the diurea compound has preferably 6 or 7 carbon atoms.

In a preferred embodiment of the present invention the urea derivativethickener is selected from the group comprising urea complex thickeners.Urea complex thickeners are defined as a mixture of at least one ureaderivative thickener with any further kind of thickener, especiallycalcium-based thickeners. Especially preferred as a urea complexthickener in accordance with the present invention is a mixture of aurea derivative thickener as defined above with at least one calciumcomplex thickener and/or calcium thickener (calcium-based thickeners).

In the sense of the present invention, a calcium thickener (soap) is areaction product of at least one fatty acid with calcium hydroxide.Preferably, the thickener may be a simple calcium soap formed from12-hydroxy stearic acid or from other similar fatty acids or mixturesthereof or methylesters of such acids. Alternatively, a calcium complexthickener (soap) may be used formed for example from a mixture oflong-chained fatty acids together with a mixture of short and/or mediumchained carboxylic acids. However, mixtures of all of the aforesaidthickeners may also be used.

The urea derivative thickener may be present in the grease compositionclaimed in an amount of about 1% by weight to about 25% by weight,referred to the total amount of the grease composition, most preferredin an amount of about 3% by weight to about 11% by weight, referred tothe total amount of the grease composition.

In a further embodiment of the present invention, the grease compositionclaimed further comprising at least one zinc dithiophosphate, molybdenumdithiocarbamate and/or molybdenum dithiophosphate as an additivepackage. Preferably, the amount of zinc dithiophosphates, molybdenumdithiophosphates and/or molybdenum dithiocarbamates is in a range ofbetween about 0.1% by weight to about 7% by weight, preferably to about5% by weight, more preferably about 0.3% by weight to about 2% byweight, in each case referred to the total amount of the greasecomposition. Most preferably, the weight percent added, referred to thetotal amount of the grease composition, of each of zincdithiophosphates, molybdenum dithiophosphates and/or molybdenumdithiocarbamates is essentially identical. In such an embodiment of thepresent invention, preferably the amount of the zinc dithiophosphates,molybdenum dithiophosphates and/or molybdenum dithiocarbamates is about0.4% by weight, 0.5% by weight, 0.6% by weight, and/or 0.7% by weight,in each case referred to the total amount of the grease composition.

In a preferred embodiment of the present invention, the furthermolybdenum containing compound is selected from the group comprisingmolybdenum dithiocarbamates and/or molybdenum dithiophosphates. The atleast one molybdenum dithiophosphate (MoDTP) and/or molybdenumdithiocarbamate (MoDTC) is preferably present in the grease compositionaccording to the present invention in an amount in a range between about0.3% by weight, more preferred about 0.5% by weight, most preferredabout 1.5% by weight, to about 3.5% by weight, most preferred about 3%by weight, in each case referred to the total amount of the greasecomposition. However, also any further molybdenum containing compoundmay be present in the grease composition according to the presentinvention as component c), of which organic molybdenum compounds arepreferred. The grease composition according to the present invention maycontain one or more MoDTC and/or MoDTP, and especially mixtures thereof.The MoDTP according to the present invention is of the following generalformula:

wherein X or Y represents S or O and each of R¹ to R⁴ inclusive may bethe same or different and each represents a primary (straight chain) orsecondary (branched chain) alkyl group having between 6 and 30 carbonatoms.

The MoDTC according to the present invention is of the following generalformula:

[(R⁵)(R⁶)N—CS—S]₂—Mo₂O_(m)S_(n)  (III)

wherein R⁵ and R⁶ each independently represents an alkyl group having 1to 24, preferably 3 to 18 carbon atoms; m ranges from 0 to 3 and nranges from 4 to 1, provided that m+n=4.

The grease composition comprises in the additive package at least onezinc compound additive, more preferably a zinc compound additive in anamount of about 0.1% by weight to about 3.5% by weight, preferably toabout 2.5% by weight, more preferably to about 0.5% by weight to about2.0% by weight, referred to the total amount of the grease composition.Most preferred the zinc compound additive is selected from the groupcomprising at least one of zinc dithiophosphates (ZnDTP) and/or zincdithiocarbamates (ZnDTC), and ZnDTPs are most preferred. The zincdithiophosphate is preferably selected from the group of zincdialkyldithiophosphate of the following general formula:

(R⁷O)(R⁸O)SP—S—Zn—S—PS(OR⁹)(OR¹⁰)  (IV)

wherein each of R⁷ to R¹⁰ inclusive may be the same or different andeach represents a primary or secondary alkyl group of which primaryalkyl groups are most preferred having 1 to 24, preferably 3 to 20, mostpreferably 3 to 5 carbon atoms. In particular, excellent effects can beexpected if the substituents R⁷, R⁸, R⁹ and R¹⁰ represent a combinationof primary and secondary alkyl groups, each having 3 to 8 carbon atoms.

The zinc dithiocarbamate may be preferably selected from zincdialkyldithiocarbamate of the following general formula:

wherein R, R¹¹, R¹², R¹³, and R¹⁴ may be same or different and eachrepresents an alkyl group having 1 to 24 carbon atoms or an aryl grouphaving 6 to 30 carbon atoms.

By adding at least one zinc compound additive to the grease compositionaccording to the invention, the friction coefficient as well as the wearin CVJ are diminished further significantly.

According to a further embodiment of the present invention, the greasecomposition may further comprise an agent comprising at least oneanti-oxidation agent, corrosion inhibitor, anti-wear agent, wax,friction modifier, and/or extreme pressure agent (EP agent), that mayalso be part of the additive package. The additive package, thus, maynot only comprise zinc dithiophosphates, molybdenum dithiocarbonatesand/or molybdenum dithiophosphates, but also the aforesaid agents.

The EP agent is preferably a metal-free polysulfide or a mixturethereof, e.g. sulphurised fatty acid methyl ester agents, withpreferably a viscosity of about 25 mm²/s at 40° C., being presentpreferably in an amount between about 0.1 to about 3% by weight,preferably 0.3 to about 2% by weight, referred to the total amount ofthe grease composition. The total inactive sulphur amount of the EPagent at room temperature preferably ranges from about 8 to about 50% byweight, preferably to about 45% by weight. The active sulphur amount asmeasured in accordance with ASTM D1662 may be about up to 11% by weight,preferably up to about 8% by weight at 100° C., and preferably up toabout 20% by weight at 140° C., the weight percent being referred to theamount of the EP agent itself. Such EP agents exhibit excellent effectswith respect to the prevention of scuffing of contacting CVJ internalcomponents. If the sulphur content exceeds the upper limit definedabove, it may promote the initiation of rolling contact fatigue and wearof the contacting metal components and may lead to degradation of theCVJ boot material.

As an anti-oxidation agent, the grease composition of the presentinvention may comprise an amine, preferably an aromatic amine, morepreferably phenyl-α-naphthylamine or di-phenylamine or derivativesthereof. The anti-oxidation agent is used to prevent deterioration ofthe grease composition associated with oxidation. The grease compositionaccording to the present invention may range between about 0.1 to about2% by weight, referred to the total amount to the grease composition, ofan anti-oxidant agent in order to inhibit the oxidation degradation ofthe base oil composition, as well as to lengthen the life of the greasecomposition, thus prolonging the life of the CVJ.

Typically, the last operation before the assembly of CVJ is a wash toremove machining debris, and it is therefore necessary for the grease toabsorb any traces of remaining water and to prevent the water fromcausing corrosion and adversely effecting the performance of the CVJ,thus a corrosion inhibitor is required. As a corrosion inhibitor, thegrease composition according to the present invention may comprise atleast one metal or dimetal salt selected from the group consisting ofmetal salts of oxidised waxes, metal salts of petroleum sulphonates,especially prepared by sulphonating aromatic hydrocarbon componentspresent in fractions of lubricating oils, and/or metal salts of alkylaromatic sulphonates, such as dinonylnaphthalene sulphonic acids,alkylbenzene sulphonic acids, or overbased alkylbenzene sulphonic acids.Examples of the metal salts include sodium salts, potassium salts,calcium salts, magnesium salts, zinc salts, quaternary ammonium salts,the calcium salts being most preferred. Calcium salts of oxidised waxesalso ensure an excellent effect. Especially preferred is disodiumsebacate as corrosion inhibitor.

Anti-wear agents according to the present invention prevent ametal-to-metal contact by adding film-forming compounds to protect thesurface either by physical absorption or chemical reaction.ZnDTP-compounds may also be used as anti-wear agents. As anti-corrosionagents according to the present invention preferably calcium sulphonatesalts are used, preferably an amount between about 0.5 to about 3% byweight, referred to the total amount of the grease composition.

As a wax compound, the grease composition of the present invention maycomprise any kind of waxes, preferably oiliness waxes, known in thestate of the art to be used in grease composition or mixtures thereof,of which montan waxes, especially ester montan waxes being a reactionproduct of at least one acid montan wax with an ester, and polyolefinwaxes including micronized montan and/or polyolefin waxes, or mixturesthereof are most preferred. Montan waxes in the sense of the presentinvention preferably comprise esters of C₂₂-C₃₄-fatty acids and probablywax alcohols having 24 to 28 carbon atoms. Esters may be present in themontan wax in accordance with the present invention in an amount in arange of about 35% by weight to about 70% by weight. Further, free fattyacids as well as free wax alcohols as well as montan resins may bepresent. Useful montan waxes are offered for example by the companyClariant GmbH, 86005 Augsburg, Germany, especially montan waxes offeredand sold under the trade name “Licowax”. Usable polefin waxes in thesense of the present invention are especially polypropylene and/orpolyethylene waxes or mixtures thereof, also including modifiedpolyolefin waxes, obtained especially by copolymerization of ethylenewith useful comonomers like vinyl esters or acrylic acid. The wax haspreferably a viscosity of at least about 50 mPa·s at 100° C., morepreferred of at least about 100 mPa·s at 100° C., and most preferred ofat least about 200 mPa·s at 100° C., measured in accordance with DIN 53018. The wax used in the grease composition may be supplied as a powderor flakes, and is added to the grease composition with a long period ofstirring, preferably at elevated temperatures, especially attemperatures about 80° C. to about 100° C.

Traditional friction modifiers used in the present invention such asfatty acid amides and fatty amine phosphates have been used in greasesand other lubricants for many years (see, e.g., the modifiers disclosedin Klamann, Dieter—“Lubricants”, Verlag Chemie GmbH 1983, 1st edition,chapter 9.6). Their role is to give the lubricant stable but notnecessarily low friction over a wide range of operating conditions.

In a preferred embodiment of the present invention, the greasecomposition claimed comprises about 50% by weight to about 98.9% byweight of the base oil composition, about 0.1% by weight to about 5% byweight of at least one tri-nuclear molybdenum compound, about 1% byweight to about 25% by weight of at least one urea derivative thickener.Most preferred, the grease composition according to the presentinvention comprises about 55% by weight to about 98.1% by weight,preferably to about 97.8% by weight, more preferred to about to 92.8% byweight, most preferred to about 92.5% by weight of the base oilcomposition, about 0.1% by weight to about 5% by weight, preferablyabout 0.3% by weight to about 2% by weight, of the tri-nuclearmolybdenum compound, about 1% by weight to about 25% by weight of theurea derivative thickener, about 0.5% by weight to about 15% by weightof at least one calcium complex thickener, about 0.1% by weight to about5% by weight of at least one ZnDTPs, about 0.1% by weight to about 5% byweight of at least one MoDTPs, and about 0.1% by weight to about 5% byweight of at least one MoDTCs. A urea derivative thickener may bepresent in a range between about 5 to about 20% by weight. Mostpreferred is a grease composition comprising about 70% by weight,preferably about 80% by weight, to about 92% by weight, preferably toabout 92.4% by weight, more preferred to about 92.7% by weight, of thebase oil composition, about 0.3% by weight to about 2% by weight,preferably to about 1.2% by weight of the least one tri-nuclearmolybdenum compound, about 4.5% by weight to about 20% by weight,preferably to about 11% by weight, of the least one urea derivativethickener, about 1.5% by weight to about 3.5% by weight of at least onemolybdenum dithiocarbamate, about 0.5% by weight to about 3% by weightof the least one zinc dithiophosphate, and about 0.5% by weight to about2% by weight of at least one wax. Further, 0.3% by weight to about 2% byweight of an EP additive are preferably added.

Preferably the grease composition in accordance with the presentinvention is characterized in that the weight percent added, referred tothe total amount of a grease composition, of tri-nuclear molybdenumcompounds is essentially identical with the weight per cent of each oneof zinc dithiophosphate, molybdenum dithiophosphate and/or molybdenumdithiocarbamate added. The compounds mentioned before may also becomposed of different zinc dithiophosphates, molybdenum dithiophosphatesand/or molybdenum dithiocarbamates, and, thus, they may present amixture of different zinc dithiophosphates, molybdenum dithiophosphatesand/or molybdenum dithiocarbamates. For clarification purposes it isnoted that the essential identity of the weight percent of thetri-nuclear molybdenum compound or mixtures of such compounds addedrefers to each one of the compounds added, and not to mixtures of thedifferent compounds mentioned. In a further referred embodiment of thepresent invention, the grease composition is characterized in that theweight percent added, referred to the total amount of the greasecomposition, of tri-nuclear molybdenum compound or mixtures of differenttri-nuclear molybdenum compounds is 4 to 10 times lower than the weightpercent of all of zinc dithiophosphate, molybdenum dithiophosphateand/or molybdenum dithiocarbamate added. If, for example, in the greasecomposition 2 weight % dithiophosphate(s) and 1 weight % molybdenumdithiocarbamate(s) are present as well as 0.5 weight % of a tri-nuclearmolybdenum compound, thus, the weight percent of the tri-nuclearmolybdenum compound added is 6 times lower than the weight percent ofzinc dithiophosphate(s) and molybdenum dithiocarbamate(s) added. It hasto be noted that also the zinc dithiophosphate, molybdenumdithiophosphate and/or molybdenum dithiocarbamate may be present asmixtures of said compounds having different structural formulas.

Further, the grease composition according to the present invention has asliding friction coefficient of not more than 0.08, as measured with aSRV test.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates the friction coefficient as a function of greasesample;

FIG. 1B illustrates the welding load as a function of grease sample;

FIG. 2A illustrates the friction coefficient as a function of greasesample;

FIG. 2B illustrates the welding load as a function of grease sample;

FIG. 3A illustrates the friction coefficient as a function of greasesample;

FIG. 3B illustrates the welding load as a function of grease samples;

FIG. 4 illustrates the friction coefficient as a function of greasesample; and

FIG. 5 illustrates the wear as a function of grease sample.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to determine the effect of the lowering of the frictioncoefficient as well as the wear by the grease composition according tothe invention, SRV tests are carried out using an Optimol InstrumentsSRV tester. Flat disc lower specimen made of the 100Cr6 standard bearingsteel from Optimol Instruments Prüftechnik GmbH, Westendstrasse 125,Munich, properly cleaned using a solvent are prepared and contacted withthe grease composition to be examined. The SRV test is an industrystandard test and is especially relevant for the testing of greases forCVJ. The test consists of an upper ball specimen with a diameter of 10mm made from 100Cr6 bearing steel reciprocating under load on the flatdisc lower specimen indicated above. In tests for mimicking tripodjoints a frequency of 7 Hz (for examples D1 and D2 only) and 40 Hz,respectively, with an applied load of 200 N were applied for 60 minutes(including running-in) or 3 hours (for examples D1 and D2 only) at 80°C., or 40° C. (examples D1 and D2). The stroke was 0.5 mm (for examplesD2 and D2 only), 1.5 mm and 3.0 mm, respectively. The frictioncoefficients obtained were recorded on computer. For each grease, thereported value is an average of four data (two data for examples D1 andD2) at the end of tests in four runs or two runs, respectively (two runsat 1.5 mm stroke and two runs with 3.0 mm stroke with the exception ofexamples D1 and D2 with two runs with 0.5 mm stroke). Wear is measuredusing a profilometer and a digital planimeter. By using theprofilometer, a profile of the cross section in the middle of the wornsurfaces can be obtained. The area (S) of this cross section can bemeasured by using the digital planimeter. The wear quantity is assessedby V=Sl, where V is the volume of the wear and l is the stroke. The wearrate (W_(r)) is obtained from W_(r)=V/L [μm³/m], where L is the totalsliding distance in the tests. For the running-in, it is started with anapplied load of 50 N for 1 minute under the above-specified conditions.Afterwards, the applied load is increased for 30 seconds by 50 N up to200 N.

Further, the welding load exerted on CVJs with a different greasecomposition is measured in accordance with a bear 4 ball EP testaccording to standard IP-239 (Energy Institute, London, UK).

The following substances are used in the examined grease compositions:

Base Oil Composition (Oil Blend)

The base oil compositions used have a kinematic viscosity of betweenabout 32 and about 250 mm²/s at 40° C. and between about 5 and about 25mm²/s at 100° C. Two base oil blends are used in this invention. Thebase oil blend A is a mixture of one or more naphthenic oils in a rangebetween about 10 to about 60% by weight, one or more paraffinic oils ina range between about 30 to about 80% by weight and one or morepoly-alpha-olefins (PAO) in a range between about 5 to about 40% byweight, referred to the total amount of the oil mixture. Oil blend Adoes not contain an organic synthetic ester, whereas oil blend Bcontains DOS in a range between about 2 to about 10% by weight referredto a total amount of the oil mixture.

The naphthenic oils are selected with a range of viscosity between about20 to about 180 mm²/s at 40° C., paraffinic oils between about 25 toabout 400 mm²/s at 40° C., and PAO between about 6 and about 40 mm²/s at100° C.

Tri-Molecular Molybdenum Compound (TNMoS)

The tri-molecular molybdenum compound used in the grease compositionsaccording to the present invention is a sulphur-containing tri-nuclearmolybdenum compound obtainable under the trade name C9455B by InfineumInternational Ltd., UK. Its structure is defined in U.S. Pat. No.6,172,013 B1.

Further Molybdenum Compounds

A molybdenum dithiophosphate (MoDTP) sold under the commercial nameSakuralube 300 (S-300) by Asahi Denka Co. Ltd., Japan, with the chemicalformula 2-Ethylhexyl molybdenum dithiophosphate, diluted with mineraloil, is used. Further, a molybdenum dithiocarbamate (MoDTC) sold underthe trade name Sakuralube 600 (S-600) in the solid state, produced byAsahi Denka Co. Limited, Japan, is used.

Zinc Compound Additive

As zinc compound additives, ZnDTP, sold by Infineum International Ltd.,Oxfordshire, UK, under the trade name C9425, is used, being a zincdialkyldithiophosphate with primary and/or secondary alkyl groups,especially having 3 to 8 C-atoms, preferably having 4 to 5 C-atoms,diluted with mineral oil.

Thickener

The urea thickener (“Thickener” in the examples) manufactured by thecompany Kyodo Yushi Co., Ltd., Tokyo, Japan, is used as defined in U.S.Pat. No. 5,589,444 (hereinafter referred to as Thickener), and is areaction product of (4,4′-Methylenediphenyl diisocyanate) withoctadecylamine.

Further, a calcium complex thickener (Calcium complex thickener) being areaction product of calcium hydroxide with two carboxylic acids, onewith a short carbon chain length of 2 to 5 carbon atoms and one with along carbon chain length of 16 to 20 carbon atoms, in which the short tolong chain ratio is between 1:2 and 1:5 is used. Examples havingmixtures containing a urea thickener as well as a calcium complexthickener, thus, comprising a urea complex thickener in accordance withthe definition in the present invention.

Wax

As wax compound, an oiliness montan wax sold by Clariant GmbH, Augsburg,Germany, under the trademark “Licowax OP” being an ester montan wax,partially saponified, with a drop point about 100° C. (DIN 51 801/1 orASTM D 127) and a viscosity of about 300 mPa*s at 120° C. (DIN 53 018)is used (“Montan wax” in the examples).

Corrosion Inhibitor

As a corrosion inhibitor, disodium sebacate is used.

Anti-Oxidation Agent

As an anti-oxidation agent (Anti-Oxidant), a diphenylamine with butyl-and/or octyl groups is used, supplied by Ciba Speciality Chemicals,Switzerland, under the trade name “L57” (Irganox L57).

EP Additive

As an EP-agent, a sulphurized organic compound (Di-t-butyl Polysulfide)sold under the trade name C9002 by Infineum International Ltd.,Oxfordshire, UK, with an inactive sulphur amount of about 45% (“EPadditive” in the examples)) at room temperature (20° C. or 25° C.) andan active sulphur amount at 100° C. of about 5% by weight, and at 140°C. of about 15% by weight, the weight percent referred to the amount ofthe EP agent itself, is used.

First, the advantages of the grease composition according to the presentinvention were examined by measuring the friction coefficient and thewelding load. Six different grease compositions were produced, as listedin Table 1:

TABLE 1 Grease Composition Example Example Example Example ExampleExample [wt %] A1 A2 A3 A4 A5 A6 TNMoS 0.5 0.5 0.5 0.5 0.5 0.5 ZnDTP 0.50.5 0.5 — 0.5 0.5 MoDTP 0.5 0.5 — 0.5 — 0.5 MoDTC 0.5 0.5 — 0.5 0.5 —Calcium complex 3.0 — 3.0 3.0 3.0 3.0 thickener oil blend 87 90 88 85 8585 Thickener 8 8 8 8 8 8

The results from the SRV-measurements of the friction coefficient aswell as the welding load measurements of examples A1 to A6 may bederived from FIG. 1. Example A2 does not contain any calcium complexthickener and/or calcium thickener, and, thus, does not comprise a ureacomplex thickener, whereas the other examples comprise an urea complexthickener. Further, the amounts of the additive package as well as thecomposition of the same are amended in examples A1 to A6. The frictioncoefficient of example A1 is below 0.06, and is the lowest frictioncoefficient measured in said test series. The friction coefficient ofexample A2 is above 0.08, and is the highest friction coefficientmeasured. Further, also the friction coefficients of examples A4 and A5are slightly higher than the friction coefficients of examples A1, A3and A6. One may derive from the friction coefficient measurements thatthe addition of an additive package containing at least one ZnDTP, atleast one MoDTP, and at least MoDTC gives the lowest values for thefriction coefficient. Further, the addition of at least one ZnDTP aswell as at least one MoDTP, preferably in combination with each other(see example A6), is preferred.

From the measurements of the welding load in FIG. 1 b) one may derivethat the welding load of example A1 as well as example A5 is higher thanthe welding load measured for the other examples. Thus, the greasecomposition according to example A1 shows the best values not only forthe friction coefficient, but also with respect to the welding load,and, thus, exhibits a good extreme pressure performance.

In a further series of tests, the amount of the TNMoS as well as theadditive package composition is amended. Three grease compositions wereprepared in accordance with Table 2.

TABLE 2 Grease Composition Example Example Example [wt %] B1 = A1 B2 B3TNMoS 0.5 1.0 0.1 ZnDTP 0.5 1.0 0.1 MoDTP 0.5 1.0 0.1 MoDTC 0.5 1.0 0.1Calcium complex 3.0 3.0 3.0 thickener oil blend 87 85 88.6 Thickener 8 88

In all of the examples B1 to B3, the amount of the thickener remainsunamended, whereas the amount of the TNMoS compound as well as thecomponents of the additive package were amended to 0.1% by weight, 0.5%by weight and 1.0% by weight, respectively, in each case referred to thetotal amount of the grease composition. The results from the SRVmeasurements with respect to the friction coefficient as well as thewelding load may be derived from FIG. 2.

Example B1 (=A1) shows the lowest friction coefficient and highestwelding load, and, thus, exhibits a very good extreme pressureperformance when compared to examples B2 and B3. Further, the loweringof the amount of the TNMoS compound as well as the components of theadditive package at values around 0.1% by weight clearly results in anincrease of the friction coefficient and a decrease in the welding load.Thus, at least about 0.25% by weight of the TNMoS compound as well as atlest one of ZnDTPs, MoDTPs and MoDTCs should preferably be present inthe grease composition.

In a third test series, the effect of the addition of a calcium complexthickener added to four grease compositions C1 to C4 in accordance withTable 3 is studied.

TABLE 3 Grease Composition Example Example Example Example [wt %] C1 =A1 C2 = A2 C3 C4 TNMoS 0.5 0.5 0.5 0.5 ZnDTP 0.5 0.5 0.5 0.5 MoDTP 0.50.5 0.5 0.5 MoDTC 0.5 0.5 0.5 0.5 Calcium complex 3.0 1.5 15 thickeneroil blend 87 90 88.5 75 Thickener 8 8 8 8

Example C2 is identical to example A2. One may derive from the SRVmeasurements of the friction coefficient as well as the measurement ofthe welding load (see FIG. 3) that the addition of 3% by weight calciumcomplex thickener resulted in the lowest friction coefficient values anda welding load above 3000 N. The welding load is especially increased byadding 15% by weight calcium complex thickener in accordance withexample C4, however, also the friction coefficient is increased tovalues about 0.08. This third test series indicates that the amount ofcalcium complex thickener used in the grease composition may be in arange of about 0.5% by weight to about 20% by weight, preferably toabout 15% by weight, thus forming a urea complex thickener with theThickener.

Further preferred grease compositions are grease compositions as listedin Table 4.

TABLE 4 Grease Composition Example Example [wt %] D1 D2 TNMoS 0.5 0.5ZnDTP 1.0 2.0 MoDTC 2.5 2.5 Montan Wax 1.0 1.0 Corrosion inhibitor 0.20.2 Anti-oxidant 0.5 0.5 EP additive 0.5 Oil blend 88.3 86.8 Thickener 66

As may be derived from FIG. 4, the friction coefficient of example D2 isbelow 0.05, and even lower than the friction coefficient of example C1.Further, the wear of example D2 is not detectable. Thus, the adding ofan EP additive as well as the increase in ZnDTP amount lead to a greasecomposition with highly preferred properties, when comprising D1 and D2.

In summary, the grease composition according to the present inventionhas an advantageous significant influence on the friction coefficientand wear, leading to a good extreme pressure performance as well as agood NVH performance in CVJs.

1. A grease composition for use in constant velocity joints comprising:a) a base oil composition; b) at least one tri-nuclear molybdenumcompound of the formulaMo₃S_(k)L_(n)Q_(z), wherein L are independently selected ligands havingorgano groups with a sufficient number of carbon atoms to render thecompound soluble or dispersible in the oil, n is from 1 to 4, k variesfrom 4 though 7, Q is selected from the group of neutral electrondonating compounds such as amines, alcohols, phosphines, and ethers, andz ranges from 0 to 5 and includes non-stoichiometric values; c) at leastone urea derivative thickener.
 2. A grease composition according toclaim 1, characterised in that the urea derivative thickener is selectedfrom the group comprising di-urea and/or polyurea compounds and mixturesof said compounds with calcium-based thickeners.
 3. A grease compositionaccording to claim 1, further comprising at least one zincdithiophosphates, molybdenum dithiocarbamate and/or molybdenumdithiophosphates.
 4. A grease composition according to claim 3,characterised in that the amount of zinc dithiophosphates, molybdenumdithiophosphates and/or molybdenum dithiocarbamates is in a range ofbetween 0.1% by weight to 5% by weight, referred to the total amount ofthe grease composition.
 5. A grease composition according to claim 4,characterised in that the weight percent added, referred to the totalamount of the grease composition, of each of zinc dithiophosphates,molybdenum dithiophosphates and/or molybdenum dithiocarbamates isessentially identical.
 6. A grease composition according to claim 1,further comprising an agent having at least one anti-oxidation agent,corrosion inhibitor, anti-wear-agent wax, friction modifier and/orextreme pressure agent (EP agent).
 7. A grease composition according toclaim 1, comprising 50% by weight to 98.9% by weight of the base oilcomposition, 0.1% by weight to 5% by weight of at least one tri-nuclearmolybdenum compound, 1% by weight to 25% by weight of at least one ureaderivative thickener, in each case referred to the total amount of thegrease composition.
 8. A grease composition according to claim 1,comprising 70% by weight to 92% by weight of the base oil composition,0.3% by weight to 2% by weight of the least one tri-nuclear molybdenumcompound, 4.5% by weight to 20% by weight of the least one ureaderivative thickener, 1.5% by weight to 3.5% by weight of at least onemolybdenum dithiocarbamate, 0.5% by weight to 3% by weight of the leastone zinc dithiophosphate, and 0.5% by weight to 2% by weight of at leastone wax.
 9. A grease composition according to claim 3, characterised inthat the weight percent added, referred to the total amount of thegrease composition, of tri-nuclear molybdenum compounds is essentiallyidentical with the weight percent of each one of zinc dithiophosphates,molybdenum dithiophosphates and/or molybdenum dithiocarbamates added.10. A grease composition according to claim 3, characterised in that theweight percent added, referred to the total amount of the greasecomposition, of tri-nuclear molybdenum compounds is four to ten timeslower than the weight percent of the total amount of zincdithiophosphates, molybdenum dithiophosphate and/or molybdenumdithiocarbamate added.
 11. A grease composition according to claim 1,characterised in that the sliding friction coefficient is at most 0.08.